PROJECT SUMMARY The form of an organ defines its function. How simple epithelial tissues give rise to the complex forms of mature organs is a fundamental question in developmental biology with important implications in disease and regenerative medicine. A beautiful example is the remodeling of a simple embryonic epithelium to form the three semicircular canals (SCC) of the inner ear. Their intricate form is required for sensing balance and acceleration and is conserved across all jawed vertebrates. SCCs can develop abnormally in congenital syndromes such as LAMM, CHARGE and Alagille syndrome, for unknown reasons. The mechanisms underlying healthy development are poorly understood. My preliminary findings indicate that local synthesis of a hyaluronan-rich extracellular matrix (ECM) is important in SCC development. In the proposed research, I will determine how this ECM helps generate mechanical forces in SCC morphogenesis in zebrafish (Aim1). I will use next-generation single-cell sequencing to identify genes involved in the patterning of an active ECM (Aim2) and to identify and characterize the role of other ECM components involved in SCC development (Aim3). The novel molecular- mechanical principles revealed from this study will be widely applicable to other morphogenetic events involving an active ECM and topological epithelial remodeling. Moreover, as these processes are disrupted in many congenital diseases and ear disorders, my findings will improve our understanding of these diseases. The proposed research draws on 1) my training in quantitative cell biology in a development context, 2) the new skills acquired in my post-doctoral research, including zebrafish research and imaging of the developing organ at single-cell resolution, and 3) my K99 training plan to implement automated image analysis, in vivo biophysical measurements, modeling, and single-cell sequencing and analysis. To fulfil my aims, I will receive mentorship from Drs. Sean Megason, Tim Mitchison, L. Mahadevan and Allon Klein, whose combined expertise in zebrafish development, gene-editing, biophysics, quantitative imaging, modeling and single-cell RNA sequencing will give me the training I need to commence my independent research program. To facilitate my career development during the mentored K99 phase, I will take relevant courses and maintain collaborations for both fundamental and translational research, present my work at meetings, publish my research, write grants, and gain further experience in management and mentoring students to formulate my own mentoring style. I will greatly benefit from the experience, track record and regular feedback from my co-mentors to start my own laboratory. My long-term career goal is to head an inter-disciplinary research program to investigate the mechanical and molecular basis of morphogenesis and to use the insights I develop to advance translational research. I?ve made significant progress towards this goal in the form of research experience, successful collaborations and publications. The K99 award will give me access to the additional training and expertise I need to successfully transition to independence.